apply powershell script to multiple xml files

I have a Powershell script that queries an xml document and outputs the results to a csv file. The script works but I need to apply it to multiple xml files in a folder and output the combined results to a csv. How can this script be modified to do this? Thanks

$xml = [XML](Get-Content D:demo\test.xml) #load xml document

#this finds file names of yearbook picks
$picks = $xml.Client.Order.Ordered_Items.Ordered_Item |
    Where-Object { $_.Description -eq 'yearbook Luster Print' } |
        ForEach-Object { $_.Images.Image_Name }


# this finds the Album
$album = $xml.SelectSingleNode("//Album_ID").InnerText -split '_'

$results = New-Object PSObject -Property @{
      Last= $album[0]
      First= $album[1]
      Code= $album[2]
      Pick1= $picks[0]
      Pick2= $picks[1]
    }

#output CSV File
$results | Export-Csv -path D:\demo\myoutput.csv -NoTypeInformation